Texas state Rep. Joaquín Castro addresses a crowd of volunteers at the Obama for America West office in Denver, Saturday, Oct. 6, 2012, before the group begins canvasing the streets to register people to vote in the Nov. 6 general election.

Texas state Rep. Joaquín Castro addresses a crowd of volunteers at the Obama for America West office in Denver, Saturday, Oct. 6, 2012, before the group begins canvasing the streets to register people to vote

Texas state Rep. Joaquín Castro addresses a crowd of volunteers at the Obama for America West office in Denver, Saturday, Oct. 6, 2012, before the group begins canvasing the streets to register people to vote in the Nov. 6 general election.

Texas state Rep. Joaquín Castro addresses a crowd of volunteers at the Obama for America West office in Denver, Saturday, Oct. 6, 2012, before the group begins canvasing the streets to register people to vote

Texas state Rep. Joaquín Castro waves after addressing a crowd of volunteers at the Obama for America West office in Denver, Saturday, Oct. 6, 2012, before the group begins canvasing the streets to register people to vote in the Nov. 6 general election.

Texas state Rep. Joaquín Castro waves after addressing a crowd of volunteers at the Obama for America West office in Denver, Saturday, Oct. 6, 2012, before the group begins canvasing the streets to register

Federico Peña, former Secretary of Transportation and former mayor of Denver, Texas state Rep. Joaquín Castro and Denver City Councilman Paul Lopez to speak to campaign volunteers at the Obama for America West office in Denver before canvasing the streets to register voters on Saturday, Oct. 6, 2012.

Federico Peña, former Secretary of Transportation and former mayor of Denver, Texas state Rep. Joaquín Castro and Denver City Councilman Paul Lopez to speak to campaign volunteers at the Obama for America

Texas state Rep. Joaquín Castro talks with volunteers before addressesing the crowd at the Obama for America West office in Denver, Saturday, Oct. 6, 2012, before the group begins canvasing the streets to register people to vote in the Nov. 6 general election.

Texas state Rep. Joaquín Castro talks with volunteers before addressesing the crowd at the Obama for America West office in Denver, Saturday, Oct. 6, 2012, before the group begins canvasing the streets to

Texas state Rep. Joaquín Castro addresses a crowd of volunteers at the Obama for America West office in Denver, Saturday, Oct. 6, 2012, before the group begins canvasing the streets to register people to vote in the Nov. 6 general election.

Texas state Rep. Joaquín Castro addresses a crowd of volunteers at the Obama for America West office in Denver, Saturday, Oct. 6, 2012, before the group begins canvasing the streets to register people to vote

State Rep. Joaquín Castro addresses a crowd of volunteers at the Obama for America West office in Denver, Saturday, Oct. 6, 2012, before the group begins canvasing the streets to register people to vote in the Nov. 6 general election.

State Rep. Joaquín Castro addresses a crowd of volunteers at the Obama for America West office in Denver, Saturday, Oct. 6, 2012, before the group begins canvasing the streets to register people to vote in the

State Rep. Joaquín Castro addresses a crowd of volunteers at the... Photo-3554988.50250 - San Antonio Express-News

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Texas state Rep. Joaquín Castro (left), canvases the Athmar Park neighborhood with Federico Peña (right), former Secretary of Transportation and former mayor of Denver, looking to register people to vote in the Nov. 6 general election in Denver on Saturday, Oct. 6, 2012.

Texas state Rep. Joaquín Castro (left), canvases the Athmar Park neighborhood with Federico Peña (right), former Secretary of Transportation and former mayor of Denver, looking to register people to vote in

Federico Peña, former Secretary of Transportation and former mayor of Denver (left foreground), and Texas state Rep. Joaquín Castro canvas the Athmar Park neighborhood looking to register people to vote in the Nov. 6 general election in Denver on Saturday, Oct. 6, 2012.

Federico Peña, former Secretary of Transportation and former mayor of Denver (left foreground), and Texas state Rep. Joaquín Castro canvas the Athmar Park neighborhood looking to register people to vote in

Federico Peña, former Secretary of Transportation and former... Photo-3554994.50250 - San Antonio Express-News

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Texas state Rep. Joaquín Castro (left) canvases the Athmar Park neighborhood with Federico Peña (right), former Secretary of Transportation and former mayor of Denver, looking to register people to vote in the Nov. 6 general election in Denver on Saturday, Oct. 6, 2012.

Texas state Rep. Joaquín Castro (left) canvases the Athmar Park neighborhood with Federico Peña (right), former Secretary of Transportation and former mayor of Denver, looking to register people to vote in

Texas state Rep. Joaquín Castro (left) canvases the Athmar Park neighborhood with Federico Peña, former Secretary of Transportation and former mayor of Denver, looking to register people to vote in the Nov. 6 general election in Denver on Saturday, Oct. 6, 2012.

Texas state Rep. Joaquín Castro (left) canvases the Athmar Park neighborhood with Federico Peña, former Secretary of Transportation and former mayor of Denver, looking to register people to vote in the Nov. 6

Texas state Rep. Joaquín Castro (right) canvases the Athmar Park neighborhood with Federico Peña, former Secretary of Transportation and former mayor of Denver, looking to register people to vote in the Nov. 6 general election in Denver on Saturday, Oct. 6, 2012.

Texas state Rep. Joaquín Castro (right) canvases the Athmar Park neighborhood with Federico Peña, former Secretary of Transportation and former mayor of Denver, looking to register people to vote in the Nov.

Texas state Rep. Joaquín Castro and Federico Peña, former Secretary of Transportation and former mayor of Denver, canvas the Athmar Park neighborhood looking to register people to vote in the Nov. 6 general election in Denver on Saturday, Oct. 6, 2012.

Texas state Rep. Joaquín Castro and Federico Peña, former Secretary of Transportation and former mayor of Denver, canvas the Athmar Park neighborhood looking to register people to vote in the Nov. 6 general

Federico Peña, former Secretary of Transportation and former mayor of Denver, shakes hands with Marvin Crumbliss as he canvases the Athmar Park neighborhood with Texas state Rep. Joaquín Castro (right). The pair were out looking to register people to vote in the Nov. 6 general election in Denver, Saturday, Oct. 6, 2012. Crumbliss, a Denver resident, was already registered to vote.

Federico Peña, former Secretary of Transportation and former mayor of Denver, shakes hands with Marvin Crumbliss as he canvases the Athmar Park neighborhood with Texas state Rep. Joaquín Castro (right). The

Federico Peña, former Secretary of Transportation and former... Photo-3554999.50250 - San Antonio Express-News

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Taboola Gallery Frame Item-85307.50250 - San Antonio Express-News

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Federico Peña, former Secretary of Transportation and former mayor of Denver (center), and Texas state Rep. Joaquín Castro talk to Marvin Crumbliss as the two canvas the Athmar Park neighborhood looking to register people to vote in the Nov. 6 general election in Denver on Saturday, Oct. 6, 2012. Crumbliss, a Denver resident, was already registered to vote.

Federico Peña, former Secretary of Transportation and former mayor of Denver (center), and Texas state Rep. Joaquín Castro talk to Marvin Crumbliss as the two canvas the Athmar Park neighborhood looking to